These are written by engineers in order to address technical risks during product discovery before we decide whether something is feasible or not.  Sometimes the engineers are trying out a new technology.  Sometimes it’s a new algorithm.   Lately it is often about assessing performance (think mobile app transitions, or Big Data).  The idea is for the developer to write just enough code to be able to answer the feasibility question.  It may be throwaway, or it might turn out to be something you can leverage if you decide to proceed.